1. Field
This invention is directed to dust covers adapted for positioning on the front fork assemblies of conventional motorcycles. More particularly, this invention is concerned with the sealing of telescopic fork tubes which make up a motorcycle front fork assembly.
2. Statement of the Art
Motorcycles and variations thereof are common and well-known in the art. In a typical construction, a motorcycle consists of a frame which is connected to two wheel support assemblies which extend from essentially opposite ends of the frame to wheel-bearing axles.
The front wheel assembly or front fork assembly may entail a variety of structural configurations. Of the known configurations, that known as a telescopic fork assembly is the most common. A telescopic fork assembly consists essentially of two parallelly oriented fork tubes or stanchions which are fixedly mounted on the frame and extend outwardly therefrom. Positioned on the lower end of each fork tube is a fork slider which, during operation of the motorcycle, is caused to move up and down on the tubes in response to road irregularities.
The fork tube assembly utilizes a spring arrangement in order to absorb shocks rendered to the motorcycle as it travels over the road. In a conventional construction, these springs are positioned within the fork tube, as well as within the fork slider. When the front fork strikes a bump in the road, the fork sliders are moved upward along the accompanying fork tube. This upward motion operates to compress the spring. When the force on the slider is released, the spring operates to forcefully return the slider to its original position. In order to avoid a rapid or sudden return of the fork slider to its original position, a dampening system is positioned within the slider/fork tube assembly.
Damper units are constructed in a variety of designs and configurations. A conventional construction utilizes a fluid medium, generally oil, which is contained within a reservoir housed in the fork tube assembly. Upon striking an irregularity in the road, the springs are compressed and, at the same time, oil is forced through a number of orifices in the damper mechanism. Upon the force being released on the fork slider, the springs operate to return the slider to its original position, requiring the oil to be siphoned back through the orifices as the slider moves down the fork tube. The resistance provided by the oil flow serves to dampen or restrict any sudden or violent extension of the slider under the action of the compressed spring.
Fork tubes are commonly hard-chromed and typically provide for an oil seal to be positioned substantially at the uppermost portions of the fork slider/fork tube assembly. This oil seal contacts or abuts against the fork tube, serving to confine the oil reservoir within the confines of the fork slider. To insulate the oil seal from contaminants, such as dirt or dust generated exterior of the fork tube assembly, a conventional practice requires the placement of a dust shield or rubber boot which is configured to be positioned about the upper end of the fork slider so as to insulate the oil seal from the environment.
As shown in FIG. 1, a dust shield typically comprises a molded rubber member having an essentially tubular cylindrical portion surmounted by a truncated, cone-like section. This shield generally includes a hollow, interior channel which is dimensioned so as to be fitted in a snug, embracing fashion over the end of the fork slider. A typical practice includes forming an annular, extension-like ring member within the bottom portion of the dust shield, which member is adapted to be fitted within a groove which is circumferentially configured into the outer surface of the fork slider. The dimension of the interior channel is such that, owing to the resilient or elastic-like properties of the rubber, it is smaller than the cross-sectional diameter of the fork slider, such that the dust shield can be expanded or stretched initially so as to receive the fork slider and thereafter contract, forming a tight, shrink-like fit around the circumference of the upper end of the fork slider.
The truncated, cone-like section of the dust shield also includes an interior channel which has a smaller diameter than the diameter of the cylindrical-shaped portion of the dust shield. This smaller diameter more closely corresponds to the diameter of the fork tube. The truncated, cone-like section adapts for positioning its interior walls in close abutment with the fork tube so as to essentially seal the opening or annular-like region which separates the fork tube and the fork slider tube.
The conventional dust shield is fabricated from rubber in view of the resilient and elastic-like properties of that material and its ability to form a substantially tight fitting seal against the fork tube and fork slider. Owing to the outdoor use of motorcycles, the rubber is exposed to the environment, and especially to the ultraviolet radiation of sunlight. These environmental factors, accompanied with the exposure to cold and heat during the varying seasons of the year, cause the rubber dust shield or boot to be subject to deterioration over time. Noticeably, the cover becomes brittle, fails to properly abut and provide a sealing action against the fork tube and/or fork slider. Eventually, after extended use, the cover ceases to render the proper dust insulating function for which it was designed.
Owing to the construction of the motorcycle, the installation of the dust shield requires essentially the complete disassembly of the front fork assembly. Noticeably, this requirement operates to disincentivize a user from making a proper and timely replacement of the shield. Absent a proper replacement of the dust shield, environmental particulates, especially dust, may thereafter be introduced through the oil seal into the oil reservoir. The contaminated oil fails to render the proper functioning and serves to complicate, if not preclude, proper operation of the slider dampening mechanism.
Of recent introduction is the use of a plated steel jacket-like member which, in exterior configuration, essentially imitates the outer configuration of the dust shield. In FIG. 1, a typical jacket is shown positioned superior to the rubber boot in the exploded view. This jacket member is configured so as to be fitted over the rubber boot and thereby insulate the boot from exposure to the environment. In other words, this jacket permits extended use life for the rubber boot in that it is substantially insulated from ultraviolet radiation or other environmentally deteriorative factors. Recognizably, the use of this jacket serves to add another component to the motorcycle assembly, and thereby increases the cost as well as the ease of maintenance and replacement of the dust shield.